20
F. M. Romero et al.
pathway, and resistance to a Fusarium-derived antibiotic. This was evidenced due to
the construction of a Tn5-mutant library, selecting mutant strains that have lost the
ability to inhibit the growth of F. graminearum.
We here described just some examples of bacterial endophytes with different
mechanisms of action, but there is a consistent reporting on the isolation of new
endophytic strains from diverse genera of plants to inhibit different phytopathogens.
Most of them demonstrated significant effects as BCAs with high levels of protection
in planta (Asghari et al. 2019; Etesami and Alikhani 2016; Ferrigo et al. 2017;
Ghazalibiglar et al. 2016; Zhang et al. 2019b). Although the exact mechanism of
biocontrol exerted by these endophytes has not fully explored so far, these constitute
a valorous collection of microorganisms for the development of biotechnological
applications (Maheshwari and Annapurna 2017).
2.3 Fungal Endophytes
The term “endophyte” is applied to fungi which has been redefined according to
the permanence of the microorganism inside host tissues, the symptomless character of the infection, and the benefits provided by the fungi to the plant host. This
is because, over the years, research regarding fungal endophytes has incorporated
functional information besides infection traits. In this trend, several functions such
as defensive mutualism, nutritional uptake, and the production of secondary metabolites improving plant fitness have been considered (Rodriguez et al. 2009; Schulz
et al. 2002). Hyde and Soytong (2008) analyzed several definitions of fungal endophytes taking into account different traits, from infection and symptom development to ecological functions. This changed the study of fungal endophytes into new
perspectives taking into consideration the permanence of mutualism, stability of the
interaction, and evolutionary features.
Fungal endophytes belong to a group with great taxonomic diversity (Arnold
et al. 2000, 2001; Rodriguez et al. 2009), which are classified according to their
identity and functional roles. Thus, fungal endophytes were divided into two groups:
Clavicipitaceous and Non-Clavicipitaceous (Rodriguez et al. 2009). Nevertheless,
it has been exhibited that most fungal endophytes studied to date corresponds to the
phylum Ascomycetes (Lugtenberg et al. 2016).
2.3.1 Clavicipitaceous Fungal Endophytes
(Grass-Endophytes Interactions)
Epichlöe-temperate grasses are the most studied models included in this category
(Omacini et al. 2012). The interactions between grasses and endophytes are clustered
in Group I, belonging to the Clavicipitaceae family in correspondence with the
F. M. Romero et al.
pathway, and resistance to a Fusarium-derived antibiotic. This was evidenced due to
the construction of a Tn5-mutant library, selecting mutant strains that have lost the
ability to inhibit the growth of F. graminearum.
We here described just some examples of bacterial endophytes with different
mechanisms of action, but there is a consistent reporting on the isolation of new
endophytic strains from diverse genera of plants to inhibit different phytopathogens.
Most of them demonstrated significant effects as BCAs with high levels of protection
in planta (Asghari et al. 2019; Etesami and Alikhani 2016; Ferrigo et al. 2017;
Ghazalibiglar et al. 2016; Zhang et al. 2019b). Although the exact mechanism of
biocontrol exerted by these endophytes has not fully explored so far, these constitute
a valorous collection of microorganisms for the development of biotechnological
applications (Maheshwari and Annapurna 2017).
2.3 Fungal Endophytes
The term “endophyte” is applied to fungi which has been redefined according to
the permanence of the microorganism inside host tissues, the symptomless character of the infection, and the benefits provided by the fungi to the plant host. This
is because, over the years, research regarding fungal endophytes has incorporated
functional information besides infection traits. In this trend, several functions such
as defensive mutualism, nutritional uptake, and the production of secondary metabolites improving plant fitness have been considered (Rodriguez et al. 2009; Schulz
et al. 2002). Hyde and Soytong (2008) analyzed several definitions of fungal endophytes taking into account different traits, from infection and symptom development to ecological functions. This changed the study of fungal endophytes into new
perspectives taking into consideration the permanence of mutualism, stability of the
interaction, and evolutionary features.
Fungal endophytes belong to a group with great taxonomic diversity (Arnold
et al. 2000, 2001; Rodriguez et al. 2009), which are classified according to their
identity and functional roles. Thus, fungal endophytes were divided into two groups:
Clavicipitaceous and Non-Clavicipitaceous (Rodriguez et al. 2009). Nevertheless,
it has been exhibited that most fungal endophytes studied to date corresponds to the
phylum Ascomycetes (Lugtenberg et al. 2016).
2.3.1 Clavicipitaceous Fungal Endophytes
(Grass-Endophytes Interactions)
Epichlöe-temperate grasses are the most studied models included in this category
(Omacini et al. 2012). The interactions between grasses and endophytes are clustered
in Group I, belonging to the Clavicipitaceae family in correspondence with the